CRT having a panel with a smaller effective area and straight outlines

ABSTRACT

In a color cathode-ray tube, the effective area of the panel is formed to be smaller than panel projected area of the apertured area of the shadow mask. The effective area of the panel having straight outlines and right-angled corners to form a rectangular shape, and each of apexes thereof coincides with that of the panel projected area. To obtain the above rectangular effective area, the present invention adopts means for restricting exposing extent between the light source and the panel, in the exposure of black matrix (FIG. 6).

TECHNICAL FIELD

The present invention relates to a color cathode-ray tube, andparticularly to a color cathode-ray tube having a novel structure and amethod appropriate for manufacturing the same.

BACKGROUND ART

A color cathode-ray tube is an apparatus for displaying a color image,in which three red, green, blue (R,G,B) phosphors are respectivelyarranged in a prescribed pattern to form a screen, and each phosphorselectively emits light by means of an electron beam.

Referring to FIG. 1, there is depicted a typical structure of the screenof a color picture tube. On the inner surface of a panel P, black matrixB is applied for enhancing the contrast excluding windows in the form ofstripes or dots, and each phosphor R,G,B is successively applied inwindows of the black matrix B. Remaining symbol A designates the metalback for forming a mirror surface, and I is an intermediate layer.

As the above described screen should be formed in a fine pitch, photolithography is generally adopted as described in FIG. 2.

Referring to FIG. 2, a slurry of black matrix B or phosphor R,G,B,including photo resist, is applied on the inner surface of a panel P ina thin layer. The panel P is placed on an exposing table, with a maskframe MF mounted in the inner side thereof as an exposure mask. The maskframe MF is formed by supporting a shadow mask M, the color selecting,means, to a frame F. Light emitted from a light source S is compensatedby a compensating lens L and exposes the applied layer of the innersurface of the panel P in a prescribed pattern determined by the shadowmask M. And the finished panel P is developed to form functional layersas in the above pattern.

These procedures are repeated four times for the black matrix B and eachof phosphors R,G,B to complete the panel as shown in FIG. 3. In FIG. 3,the screen of the panel P can be divided into a non-effective area Pnonly with the black matrix B, and an effective area having phosphorR,G,B between the black matrix B to form an image.

To compensate for the difference in distances from the center ofemission of the electron beam to the central part and thecircumferential part, the panel P is formed in a shape of a curvedsurface having prescribed curvatures respectively to the horizontal,vertical and the diagonal axis. And the shadow mask M also formed in acurved surface to maintain a prescribed gap, namely the Q value, withthe screen of the panel P.

The shadow mask M can be divided into an apertured area having colorselecting apertures to form the effective area Pe of the panel P, and anon-apertured area having no apertures to correspond to thenon-effective area Pn of the panel P.

As the shadow mask M has the curved surface, the outline O of theeffective area Pe projected on the panel P, forms the outwardly convexcurved line even in the case of the outline, of the apertured area to bestraight. As the result, the shape of the effective area Pe is definedby four lines O and four corner portions C, each of outlines O meetingtogether thereat and being rounded for continuity's sake.

Referring to FIG. 4, there is depicted a tube mounted in the casing of atelevision set or a monitor. As the outline O' of the bezzel cover Z ofthe casing is nearly straight, a part of the non-effective area Pn isexposed at the corner portion C,C' and the outline O of the panel P iscovered by the outline O' ot the bezzel cover Z at the intermediate partof the screen, thereby extremely exposing the effective area Pe in thebezzel cover Z.

As the result, a appearance of the finished display is not good, and thescreen cannot be extremely utilized. Moreover, excessive heat isradiated and severe doming occurs, as the electron beam exposes thewhole effective area Pe, which is larger than the area to actualydisplay the image.

This screen structure deteriorates the accuracy and reliability of data,especially in the CDP which takes data through the screen. To preventthese problems the outline of the shadow mask M is generally formed tobe inwardly concave for the CDT, which causes many problems in theforming of the shadow mask M.

Recently, a Flat Square Tube as shown in FIG. 5 is suggested, the tubereduces the curvature of the panel P to be flat and forms four corners Cwhich nearly are right angles, thereby making the effective area Pealmost rectangular.

The Flat Square Tube, however, requires a new panel P and a shadow maskM which are different from those of previously known tube, and the flatpanel P thereof a wholly redesigned and separately produced electron gunassembly, deflection means, and compensating means. Moreover, thecompensation of the convergence and others tend to be highly difficultas the difference of distances from the emission center of the gun tothe central part and circumferential part of the panel P.

And the shadow mask is also used as an exposure mask even in the FlatSquare Tube, thus the change of the exposure pattern due to theoccurence of doming of the shadow mask by the high heat from the lightsource, and the resultant deterioration of the color purity cannot beprevented.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a colorcathode-ray tube having a rectangular effective area as that of FlatSquare Tube, through utilizing components and procedures for a generaltube just as they are.

It is another object of the present invention to provide an appropriatemethod for manufacturing the above described color cathode-ray tube, inwhich a rectangular effective area can be achieved through componentsand procedures for a general tube just as they are, and the heatdeformation problem of the shadow mask during the exposure process canbe resolved.

A color cathode-ray tube to achieve the primary object of the presentinvention, is characterized in that:

the projected area of the apertured area of the shadow mask on thepanel, is larger than the effective area of the panel.

According to one aspect of the present invention, the apex of the cornerportion of the prejected area of the apertured area on the panelcoincides with that of the effective area of the panel, and theeffective area has almost a rectangular shape.

According to another aspect of the present invention, phosphor isapplied on the projected area of the apertured area of the shadow maskon the panel, and the outline of the effective area is confined by theblack matrix.

In a typical color cathode-ray tube, the projected area of the aperturedarea of the mask, the window forming part of the black matrix and thephosphor applied part all coincide with each other, as striped or dottedwindows are formed at the effective area of the panel, and phosphor areapplied on these windows. In contrast, the window forming part issmaller than the phosphor applying part, namely the panel projected areaof the apertured area of the shadow mask according to the presentinvention, to restrict the size and shape of the effective area.

As the result, a rectangular effective area can be obtained withcomponents of a conventional color cathode-ray tube.

A method for manufacturing the above described color cathode-ray tube,is characterized in that:

the black matrix is exposed with means for restricting the exposureextent; and

the phosphor is exposed after removing the above restricting means.

Restricting means can be embodied in an auxilliary mask mounted on theshadow mask, a restriction plate mounted in the light path of theexposing light, or in a restriction filter mounted on the lens system.

According to the present invention, heat deformation problems of theshadow mask can be remedied to form a rectangular effective area of thepanel while adopting conventional procedures of a general colorcathode-ray tube just as it is.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects and advantages will be more apparent from thefollowing detailed description with reference to the accompanyingdrawings, in which:

FIG. 1 is a sectional view depicting the structure of the phosphorscreen of a typical color cathode-ray tube;

FIG. 2 is a sectional view illustrating the production procedure of atube by the photo lithography;

FIG. 3 is a front view of the screen of a conventional color cathode-raytube;

FIG. 4 is a partially enlarged front view showing the tube being mountedin a casing;

FIG. 5 is a front view of a Flat Square Tube;

FIG. 6 is a front view of a color cathode-ray tube according to thepresent invention;

FIG. 7 is a sectional view of an exposure mechanism to produce the tubeaccording to the present invention;

FIG. 8 is a sectional view according to another method of the presentinvention;

FIG. 9 is a plan view of a restriction plate utilized in the methodshown in FIG. 8;

FIG. 10 is a sectional view according to still other method of thepresent invention;

FIG. 11 is a perspective view showing the restriction filter utilized inthe method shown in FIG. 10; and

FIG. 12 is a front view showing the present tube mounted in the casing.

MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 6, a panel projected area Pp, the area formed byprojecting a light source S through the shawdow mask M and compensatinglens L, is shaped along with the broken line according to the presentinvention. The panel projected area Pp corresponds to the effective areaPe of the conventional tube shown in FIG. 3, and has same size andshape, namely the same outline O and corner portions.

According to the present invention, black matrix B hides inner edges ofthe panel projected area Pp to form a rectangular effective area P1. Asthe result, the effective area P1 has straight outlines O1 and cornerportions C1 of right angles.

In other words, windows of the black matrix B are formed not all overthe panel projected area Pp as in the conventional tube, but only on theeffective area P1, thus making, as shown in FIG. 4, crescent shapedshaded portions between the panel projected area Pp and the effectivearea P1.

In the shaded portions, each of R,G,B phosphor is applied thereon insuccession with the effective area P1, it consists of a part ofnon-effective area P2 as it is covered by black matrix B.

As a part of the panel projected area Pp of the apertured area of theshadow mask M, is covered by black matrix, the effective area P1 is tobe smaller than the panel projected area Pp. According to the presentinvention, outwardly convexed outlines O of the conventional effectivearea Pe (equal to the panel projected area Pp) is trimmed by blackmatrix to form a rectangular shaped effective area P1.

It is preferable to make the four apexes of corner portions C of thepanel projected area Pp coincide with those of the effective area P1.When apexes of the effective area P1 are located at the inner side ofthose of the panel projected area Pp, the size of the screen is reduced.And in the opposite case the corner protions C1 are rounded.

The present color cathode-ray tube can preferably be manufactured asshown in FIG. 7.

In FIG. 7, an auxilliary mask M1 is adopted as means for restricting theexposure extent. Black matrix B is exposed through a shadow mask Mcoupled with the auxilliary mask M1 having a window W for restrictingthe extent of the exposure, and phosphors R,G,B are exposed without theauxilliary mask M1.

As the result, windows of the black matrix B are formed on the partrestricted by the window W of the auxilliary mask M1, and phosphorsR,G,B is applied on the part corresponding to the panel projected areaPp of the shadow mask M and the outer portion thereof is covered byblack matrix B to form a rectangular effective area P1.

In the drawing, the auxilliary mask M1 is depicted to be formed in theshape of a rim capable of projecting a rectangular effective area, andis coupled to the rear of the frame F of the mask frame MF. It can be,however, coupled to the front of the shadow mask M, and be formed as atransparent plate located on the face plate (not shown) of the exposuretable on which the panel P is placed. The transparent plate can be madefrom glass or synthetic resin to have an opaque layer located outside ofthe periphery of the effective area P1 for restricting the exposureextent. The auxilliary mask M1 can also be formed on an opaque tapeadhered to the face of the shadow mask M in the exposure of black matrixB, and the phosphors R,G,B are exposed after detaching the tape.

Means for restricting the exposure extent can be embodied in variousforms, the method illustrated in FIGS. 8 and 9 adopts a restrictionplate M2 mounted in the light path of the exposure light.

Referring to FIG. 8, a panel P being applied by black matrix and coupledwith the mask frame MF is placed on the exposure table, and the exposinglight generated from a light source S is projected through acompensating lens L. In the path of the exposing light, a restrictionplate M2 is mounted to restrict the extent of the exposure according tothe present invention. The restriction plate M2 has an inwardly concavedpin-cushion shaped window W as shown in FIG. 9 to make the light fromthe source S have the rectangular outline O1 as shown in FIG. 6.

After forming black matrix B with the above restriction plate M2,phosphor is formed without the plate M2 to obtain the phosphor screen asshown in FIG. 6 as a result.

In the method illustrated. in FIGS. 10 and 11, a restriction filter M3mounted on the lens system L is adopted as means for restricting theexposure extent.

Referring to FIG. 10, a panel P being applied with black matrix andcoupled with the mask frame MF, is placed on the exposure table, and theexposing light from the light source S is projected after beingcompensated its pattern through the lens system L. In the lens system L,a restriction filter M3 is mounted to restrict the exposure extentaccording to the present invention. The restriction filter M3 has aninwardly concaved pin-cushion shape window W to confine the lightprojected from the light source to have the rectangular outline O1 asshown in FIG. 6. The restriction filter M3 can be formed by partiallycoating an opaque layer F on a glass substrate, and can be formed by ametal sheet in which the window W is cut out.

After forming black matrix with the restriction filter M3, phosphor isexposed without the filter M3 to result in the phosphor screen shown inFIG. 6. In general, the exposure of black matrix and phosphor areseparately advanced at separate exposure tables, thus the abovedescribed method means the exposure extent restricting means M1˜M3 ismounted only on the exposure table of the black matrix.

In FIG. 12, there is illustrated the present color cathode-ray tubemanufactured as above, to be installed in the casing. In the drawing,the outline O1 of the effective area P1 is formed in straight lineparallel with the outline O' of the bezzel cover Z, and the right-angledcorner portion C1 thereof corresponds to the corner portion C' of thebezzel cover Z.

As described above, a rectangular screen can be obtained throughadopting components and procedures of conventional color cathode-raytube just as they are, without separately designing or producing them.This provides a color cathode-ray tube of a neat appearance and exacthandling of data, without excessive additional production cost.

Moreover, the applied area of black matrix is relatively larger than thescanning area of the electron beam, thus the heat is well discharged torestrain the occurence of doming in operation. And the thermaldeformation of the shadow mask is also suppressed during the exposingprocedure to improve the quality of the phosphor screen.

I claim:
 1. A color cathode-ray tube comprising a phosphor screen formed on an inner surface of a panel through successive photo lithography of black matrix and each phosphor by use of a color selecting shadow mask as an exposure mask, whereinan effective area of said panel is smaller than a projected area of an apertured area of said shadow mask to said panel.
 2. A color cathode-ray tube according to claim 1, whereineach apex of corner portions of said effective area coincides with each corner portion of said panel projected area.
 3. A color cathode-ray tube according to claim 1, whereinsaid effective area has a rectangular shape.
 4. A color cathode-ray tube according to claim 1, whereinsaid phosphor is applied on said panel projected area; and said black matrix covers a part of said panel projected area to form said effective area of a prescribed shape. 